Myalgic encephalomyelitis (ME), also known as Chronic fatigue syndrome (CFS), refers to a group of debilitating medical conditions characterized by persistent fatigue and other specific symptoms that last for a minimum of six months in adults (and 3 months in children or adolescents). This disease is also referred to as systemic exertion intolerance disease (SEID), post-viral fatigue syndrome (PVFS) and chronic fatigue immune dysfunction syndrome (CFIDS).
ME/CFS is characterized by persistent and debilitating fatigue, diffuse musculoskeletal pain, sleep disturbances, neuropsychiatric symptoms and cognitive impairment which cannot be explained by an underlying medical condition. The symptoms of ME/CFS are not caused by ongoing exertion and are not relieved by rest.
ME/CFS is a symptom-based diagnosis or clinical diagnosis without distinguishing physical examination or routine laboratory findings. Infectious, immunological, neuroendocrine, sleep and psychiatric mechanisms have been investigated; however, a unifying etiology for ME/CFS has not yet emerged. The majority of ME/CFS cases start suddenly and they are usually accompanied by a “flu-like illness”, while a significant proportion of cases begin within several months of severe adverse stress (Afari N et al (2003), Am J Psychiatr 160 (2): 221-36). Often, there are courses of remission and relapse of symptoms which make the illness difficult to manage. Persons who feel better for a period may overextend their activities, and the result can be a worsening of their symptoms with a relapse of the illness.
ME/CFS often occurs together with other diseases such as fibromyalgia (FM), multiple chemical sensitivities, irritable bowel syndrome and temporomandibular joint disorder. In particular, co-morbidity with fibromyalgia has been studied (Afari N et al, supra). Fibromyalgia is a nonarticular rheumatic syndrome characterized by myalgia and multiple points of focal muscle tenderness to palpation (trigger points). Patients with FM often experience muscle pain aggravated by inactivity or exposure to cold. This condition is often associated with general symptoms, such as sleep disturbances, fatigue, stiffness, headaches and occasionally depression.
Despite the contrasting definitions of the two disorders, 20-70% of patients with fibromyalgia also meet the criteria for chronic fatigue syndrome, and conversely, 35-70 of those with chronic fatigue syndrome-like illnesses have concurrent fibromyalgia (Afari N et al, supra).
ME/CFS is a common disorder. Estimates of the prevalence of ME/CFS range from 0.07% to 2.8% in the general adult population and is lower in children and adolescents (Afari N et al, supra). The prevalence of the related fibromyalgia (FM) is 2-4%. This means that in Sweden at least 40 000 patients suffer from ME/CFS and 270 000 from FM (for review see Zachrisson O (2002); Fatigue Syndrome-aspects on biology, treatment and symptom evaluation [dissertation]. ISBN 91-628-5386-4. Gothenburg University).
Many patients suffering from ME/CFS experience significant functional impairment. Nearly all patients with ME/CFS notice a decrease in social relationships in addition to other unwanted consequences of illness; about one-third are unable to work or study, and another one-third can only work part-time (Afari N et al, supra). Many patients suffering from ME/CFS also experience depression symptoms and are diagnosed with clinical depression, and likewise, patients who suffer from depression often experience symptoms of debilitating fatigue.
Currently, patients suffering from ME/CFS are treated by cognitive behavioral therapy (CBT) or graded exercise therapy (GET), which have shown moderate effectiveness in multiple randomized controlled trials, however many patients do not make recovery (Rimes K A et al (2005), Occupational Medicine 55(1): 32-39; Chambers D et al (2006). Journal of the Royal Society of Medicine 99(10): 506-20). At present, medication plays a minor role in disease management (Van Houdenhove B et al (2010) Expert opinion on pharmacotherapy 11(2): 215-23).
Additionally, many disorders, in addition to ME/CFS and FM, are characterized by symptoms of debilitating fatigue. Such disorders include mental fatigue, post stroke fatigue, Huntington's disease, Parkinson's disease, multiple sclerosis, narcolepsy, post cancer fatigue, fatigue associated with cancer with or without cytostatic treatment, depression and combinations thereof.
Thus there is a large need for novel therapies and treatments to alleviate fatigue symptoms, such as ME/CFS associated fatigue symptoms and fatigue symptoms associated with other clinical indications, and thus the provision thereof remains a matter of substantial interest within the field.